The present invention pertains to a process for changing the concentration in an anesthesia apparatus with a breathing circuit with an inspiration branch and an expiration branch, with a fresh gas metering unit and a pressure sensor in the breathing circuit, with a volume displacement means in the inspiration branch and a PEEP/PMAX valve in the expiration branch, wherein the fresh gas metering unit, the pressure sensor, the volume displacement means and the PEEP/PMAX valve are connected to an evaluating and control unit.
Anesthesia apparatus which have a volume displacement means as the breathing gas delivery unit for the tidal volume to be applied in the patient have the problem that especially at low respiratory minute volumes, i.e., at low volume displacements per minute, called RMV for short, a change in the anesthetic or fresh gas concentration reaches the patient only very slowly. The cause of this is that the anesthetic or fresh gas fed in newly is not distributed immediately uniformly in the entire breathing circuit of the anesthesia apparatus but gas segments with the new concentration, consisting of anesthetic, fresh gas and a certain percentage of expired gas, move to the patient gradually through the inspiration branch of the breathing circuit with the inspiration stroke. The gas segments with the new concentration are moving toward the patient at a speed proportional to the respiratory minute volume. If very small tidal volumes are to be applied, which occurs, e.g., in the case of neonatal respiration, and also in the case of long tubes, it may take several minutes before the change in concentration in the breathing circuit can be detected at the mouthpiece leading to the patient.
This process cannot be expedited by increasing the fresh gas supply, which will hereinafter also increase fresh gas containing an anesthetic, because anesthesia apparatus with volume displacement means usually operate uncoupled from the fresh gas. If the fresh gas supply is increased, the portion of the fresh gas supply exceeding the respiratory minute volume is discharged unused via the anesthetic gas discharge without a rapid change in concentration taking place at the mouthpiece leading to the patient.
DE 40 04 034 C2 describes an anesthesia respirator with a ventilator as a breathing gas delivery unit, with which a changed set point of an anesthetic gas component can be preset in a time-optimized manner. The control circuit for the system parameters of the breathing circuit is disconnected for a defined period of time, during which the breathing circuit can be flooded with the gaseous anesthetic to be changed. The control circuit is closed again only when a concentration value close to the new set point to be set is reached, as a result of which the controller influences the metering unit of the anesthetic gas in question for setting the new set point.
The drawback of the prior-art anesthesia respirator is that a complicated control circuit is necessary, by means of which a changed anesthetic gas concentration can be brought about in the breathing circuit.
The object of the present invention is to provide a process with which a rapid change in the concentration of the anesthetic or fresh gas being fed can be brought about in the breathing circuit of an anesthesia apparatus without additional design effort.
According to the invention, a process is provided for changing the concentration in an anesthesia apparatus with a breathing circuit. An inspiration branch and an expiration branch are provided with a fresh gas metering unit and a pressure sensor in the breathing circuit, with a volume displacement device in the inspiration branch and a PEEP/PMAX valve in the expiration branch. The fresh gas metering unit, the pressure sensor, the volume displacement device and the PEEP/PMAX valve are connected to an evaluating and control unit. The volume displacement device is completely returned, and the fresh gas supply by the fresh gas metering unit is at the same time increased via the evaluating and control unit such that the volume displacement device is completely filled with the fresh gas fed in. The volume displacement device is moved forward completely, and a set pressure preset on the PEEP/PMAX value is not exceeded in the breathing circuit.
According to another aspect if the invention, a process is provided for changing the concentration in an anesthesia apparatus with a breathing circuit. An inspiration branch and an expiration branch are provided with a fresh gas metering unit and a pressure sensor in the breathing circuit, with a volume displacement device in the inspiration branch and a PEEP/PMAX valve in the expiration branch. The fresh gas metering unit, the pressure sensor, the volume displacement device and the PEEP/PMAX valve are connected to an evaluating and control unit. The fresh gas supply from the fresh gas metering unit is set at the maximum amount that can be metered, and the volume displacement device, controlled by the evaluating and control unit, is returned at the same time at such a speed that the total amount of fresh gas fed by the fresh gas metering unit is taken up by the volume displacement device. The volume displacement device is moved completely forward, and a pressure preset on the PEEP/PMAX valve is not exceeded in the breathing circuit.
One advantage of the process according to the present invention is that a change in concentration reaches the patient very rapidly i.e., within one to three respiration cycles, doing so due to a rinsing operation during the regular operation of the anesthesia apparatus to which the patient is connected.
As an alternative, the rinsing of a volume displacement unit, which displaces the tidal volume to be applied to the patient, can be performed by complete filling with fresh gas either under the control of the fresh gas supply or under the control of the speed, at which speed the volume displacement device is returned for the fresh gas filling. The fresh gas supply and the speed of return are coordinated with one another in both cases such that the volume displacement device is filled completely with fresh gas, and the smallest possible amount of fresh gas is lost unused via the anesthetic gas discharge.
Besides the volume displacement device, the absorber can be rinsed as well. Depending on whether and how the volume displacement device is located in the inspiration branch of the breathing circuit or in another area of the breathing circuit, it must be subsequently rinsed after the rinsing of the volume displacement device, or it can be rinsed already simultaneously in the second case, as a result of which the entire process is shortened in time.
Moreover, the process according to the present invention can be used in a versatile manner, namely, for both pressure-controlled respiration and volume-controlled respiration, and only an additional process step is to be performed first in the latter case, namely, the end inspiratory pressure is measured in the breathing circuit and the measured value is stored in order to preset in the last step a maximum pressure below which the volume displacement device is moved forward. The possibility of use covers volume displacement device which displace the volume in their front range of displacement and in their rear range of displacement alike.
Further details of the present invention will be explained on the basis of the exemplary embodiment shown in the drawing.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawing and descriptive matter in which preferred embodiments of the invention are illustrated.